The atomic mass of Athenium is 230.505 amu. An isotope is a form of an element with a varying number of neutrons. Every atom has the same number of protons, and therefore electrons, but the number of neutrons may vary. The hypothetical element Athenium (Ah) exists in two isotopic forms: 86.500% abundance, relative mass of 230.145 amu and 13.500% abundance, relative mass of 231.769 amu.To determine the atomic mass of Athenium, use the formula: Atomic mass = (percent abundance 1 × relative mass 1) + (percent abundance 2 × relative mass 2) / 100Atomic mass of Athenium = (86.5 × 230.145) + (13.5 × 231.769) / 100 = 230.505 amuTherefore, the atomic mass of Athenium is 230.505 amu.